1. Field of the Invention
The invention relates to an adjustable damping valve.
2. Description of the Related Art
Vibration dampers with adjustable damping force often have an electromechanical actuator for changing the cross section of a valve opening. The concept of safety entered into the development of adjustable vibration dampers at an early point, and this led to the idea of equipping the actuator with a spring, which, if the current were interrupted, would act on a valve body to minimize the cross section of the valve opening. Reference can be made to DE 35 18 327 C2 an example. The goal was to achieve a high damping force setting, so that sufficient damping force would be available for all damping movements.
The percentage of time during which a damper acts with maximum damping force is comparatively small during normal driving. In the case of an actuator with the design according to DE 35 18 327 C2, there is the disadvantage that a large amount of actuating current is required to achieve a “soft” damping force setting, because the force of the magnetic coil must act against the force of the spring. The stronger the force of the magnetic coil, the greater the open cross section of the adjustable damping valve and the lower the obtained damping force, which leads to comfortable driving behavior.
The disadvantages associated with the design principle of this actuator led to the idea that an intermediate damping force characteristic might be better for the emergency operating mode of the adjustable vibration damper. Various design approaches have been taken, including that described in DE 39 17 064 A1.
In the variant according to FIG. 1 of DE 39 17 064 A1, a valve body 50 is used, which has two control parts 75, 76, which cooperate with valve seats 86, 88. The actuator 44, 46 must exert an opening force against the force of the restoring spring 82 in order to hold the control parts 75, 76 in the middle position for the softest damping force characteristic. When the actuator fails, the control part 76 will lie on the valve seat 88 and thus minimize the outflow from the pressure space 64. The slanted throttle point 108 and a throttle point provided with an emergency valve are then available for the outflow of the damping medium from the pressure space.
The variant according to FIG. 2 of DE 39 17 064 A1 functions in a very similar way. The difference is that a ball is used as the valve body. In addition, the throttle point 108 connected hydraulically in parallel with the valve body extends in the longitudinal direction through an intermediate wall in the damping valve. Common to both designs, however, is that, although they describe a functional principle, they do not tell how to overcome the considerable difficulties involved in achieving a technical realization of that principle, because the amount of space which is available is very small, and the degree of precision required for the components is very high. The two figures do not show the outlines of any components which make it possible to install, for example, the valve body 50.